1. Field of the Invention
The present invention relates to a metal oxide semiconductor (MOS) transistor and the manufacturing method thereof, and more particularly, to a MOS transistor having a silicide layer with a curved bottom surface and the manufacturing method thereof.
2. Description of the Prior Art
With a trend towards scaling down the size of the semiconductor devices, conventional methods are used to achieve optimization and reduce the thickness of the gate dielectric layer, like reducing the thickness of silicon dioxide layer, but have faced problems such as current leakage due to the tunneling effect. In order to keep progressing towards the next technology generation, high-k materials are used to replace the conventional silicon oxide in the gate dielectric layers, because it decreases the thickness physical limits effectively, reduces current leakage, and achieves equivalent capacitance with an equivalent oxide thickness (EOT).
On the other hand, the conventional poly-silicon gates also face problems, such as lower performance due to boron penetration, and an unavoidable depletion effect, which increases equivalent thickness of the gate dielectric layer, reduces gate capacitance, and decreases the driving force of the device. Thus, work function metals that are compatible with the high-k gate dielectric layers are developed to replace the conventional poly-silicon gates as control electrodes.
According to the fabricating sequence of the high-k dielectrics, a conventional method of forming a MOS transistor can be divided into “high-k first” processes and “high-k last” processes. In the “high-k last” processes, after forming the high-k dielectric layer, an annealing step is usually performed to improve the quality of the high-k dielectric layer. However, this annealing step may be harmful to other already-formed semiconductor components, such as silicide layer, thus influencing the quality of the MOS transistor.